Good video but couple things to be aware of, from personal experience
Butter knife.. make sure there are no serrations or "cutting" ridges on them. I cant describe them better, but if its not smooth be very very careful. They will cut skin, especially fingers & webbing in addition to cutting rubber orings. I've done both, sadly.
Instead of that jar brush try a toothbrush, a cheap plain brush, dont need fancy gum sweepers or rubber bits on the bristle end, just a cheap toothbrush. They get into the small ridges easily, can "sweep" away the mold or nasty bits. I mean they clean your teeth so heh. I use my old ones as kitchen drain scrubbers & we used to use them in the military to scrub various things other than the floor

Now I have to go get mine to see what type of cap they have, jesus this is why I trust disposable so much more, I dont have to worry about mold. Long time ago I pulled the oring outta my walmart coffee travel mug, I like em with milk but always wash them out asap. Found lots of nasty stuff caked up under the ring so now I throw them in the dishwasher top shelf basket once a week or so.